Family Xyalidae

Rev. 03/23/2023  

Nematoda

Chromadorea

Chromadoria

Monhysterida

Monhysterina

Sphaerolaimoidea

Xyalidae Chitwood, 1951

Pseudosteineria sp (Xyalidae): Cephalic setae (from Cesaroni et al., 2017)

• A widespread family of mostly marine free-living nematodes.
• Free-living nematodes of marine and brackish water; often among the most abundant of the nematode taxa in an environment..
• Body length 0.5-2 mm.
• Cuticle finely striated and with long somatic setae.
• Ocelli sometimes present.
• Mouth cavity simple, funnel-shaped, denticles either absent or minute.
• 6+4 sensillae almost always situated very close, for example, the 2nd  annule with 6 cephalic setae anf the third with 4.  There may be with additional cephalic setae.
• Esophagus cylindrical.
• Female monodelphic prodelphic, vulva at 60-65% of body length. Per Lorenzen (1994, in didelphic forms,  the anterior gonad is always on the left of the intestine and the posterior gonad on the right.
• Male with two testes, occur commonly. 
• Circular amphids, some marine forms with spiral amphids.
• Tail elongate conoid, terminated in a short spinneret..
• Many of the species descriptions of nematodes made in the 20th century were made basaed on very few specimens with relatively few characters of taxonomic value (Venekey et al., 2014). Consequently, taxonomic reviews and revisions are difficult,

References:

Cesaroni, L. Guidi, L., Balsamo, M., Semprucci, F. 2017. Scanning electron microscopy in the taxonomical study of free-living marine nematodes. Microscopie 28:6970

Fonseca, G., Bezerra, T.M. 2014. 7.14 Order Monhysterida in A. Schmidt-Rhaesa. Handbook of Zoology, Gastrotricha, Cycloneuralia and Gnathifers, Vol 2. Nematoda. De Gruyter, Berlin. 759p

Lorenzen S (1994) The phylogenetic systematics of free-living nematodes.The Ray Society Institute, London, n.162

Venekey, V., Gheller, P.F., Maria , T.F., Brustolin, M.C., Kandratavicius , N., Vieira , D.C., Brito, S., Souza, G.S., Fonseca, G. The state of the art of Xyalidae (Nematoda, Monhysterida) with reference to the Brazilian records. Marine Biodiversity DOI 10.1007/s12526-014-0226-3

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